Thirty North Korean officials, once involved in inter-Korean talks, are believed to have been executed either by firing squad or killed in staged traffic accidents, a human rights advocacy group said Thursday.

Amnesty International raised the suspicions in its annual report, citing unconfirmed reports in July. The alleged purge suggests that North Korea used the officials as scapegoats for soured inter-Korean ties.

Tensions still persist on the Korean Peninsula over the North's two deadly attacks on the South in 2010. North Korea has also ratcheted up military threats against South Korea in recent months.

It is not unusual for the communist country to execute its officials.

In 2010, the North reportedly executed Pak Nam-gi, former chief of the planning and finance department of the ruling Workers' Party, over Pyongyang's botched currency reform in 2009 that caused massive inflation and worsened food shortages.

In the 1990s, North Korea executed a top agricultural official over a massive famine that was estimated to have killed 2 million people.

In January, the North's State Security Agency detained over 200 officials in apparent preparation for a power succession following the December death of North Korea's long-time leader Kim Jong-il, Amnesty International said, citing unconfirmed reports. Kim's youngest son, Kim Jong-un, assumed power.

The London-based rights group said some of the detained officials "were feared executed, while others were sent to political prison camps."

The annual report estimated that up to 200,000 prisoners were held in horrific conditions in six sprawling political prison camps, citing "credible reports."

Thousands were also imprisoned in at least 180 other detention facilities, the annual report said, without elaborating.

North Korea has long been labeled one of the worst human rights violators in the world. The North has denied accusations of its alleged rights abuses, however, calling them a US-led attempt to topple its regime.